This application is based on Japanese Patent Application No. 2000-263195, filed in Japan on Aug. 31, 2000, the contents of which are hereby incorporated by reference.
This invention relates to a fuel supply apparatus. In particular, it relates to a high pressure fuel supply apparatus for supplying a fuel under high pressure to an internal combustion engine.
FIG. 8 schematically illustrates a typical fuel supply system for an automotive internal combustion engine equipped with fuel injectors. As shown in this figure, fuel 2 within a fuel tank 1 is discharged from the fuel tank 1 by a low pressure pump 3 and passes through a filter 4, and after its pressure is adjusted by a low pressure regulator 5, it is supplied to a high pressure fuel supply apparatus 6. The fuel is pressurized by the fuel supply apparatus 6 and is supplied to a common rail 9 of an internal combustion engine (not shown). Excess fuel not needed by the engine is transferred by an electromagnetic valve 17 to a point between a low pressure damper 12 and an intake valve 13. A control unit (not shown) determines the necessary amount of fuel to be supplied to the engine and controls the electromagnetic valve 17 accordingly. The high pressure fuel which is supplied in this manner is sprayed as a high pressure mist from fuel injectors 10 connected to the common rail 9 and is injected into cylinders (not shown) of the internal combustion engine. A high pressure relief valve 8 connected to the discharge side of the supply apparatus 6 through a filter 7 opens when there is an abnormal pressure within the common rail 9 and prevents damage to the common rail 9 and the fuel injectors 10.
The high pressure fuel supply apparatus 6 includes a filter 11 which filters the supplied fuel, the above-mentioned low pressure damper 12 which absorbs pressure pulses of the low pressure fuel, and a pump 16 which pressurizes fuel which is supplied through the intake valve 13 and discharges high pressure fuel through a discharge valve 14 and a fuel pressure maintaining valve 15.
FIG. 9 illustrates the actual structure of an example of the high pressure fuel supply apparatus 6 schematically illustrated in FIG. 8. As shown in FIG. 9, the high pressure fuel supply apparatus 6 has a casing 21 containing a cylinder 25 which defines a compression chamber 24 of a high pressure pump 16. The casing 21 also includes an intake passage 22 for fuel to be pressurized in the compression chamber 24 and a discharge passage 23 for pressurized fuel. A piston 26 in the form of a plunger is supported in the cylinder 25 for sliding movement in the axial direction thereof so as to vary the volume of the compression chamber 24. A compression spring 27 is provided at the inner end (the upper end in FIG. 9) of the piston 26, and at the outer end (the lower end in FIG. 9) an operating member in the form of a tappet 28 which receives a drive force from the camshaft of the unillustrated engine and transmits it to the piston 26 is supported by a bracket 30 for sliding movement in the axial direction of the piston 26.
The high pressure fuel supply apparatus 6 comprises, as a unitary structure, the high pressure pump 16 which is a plunger pump for example, the electromagnetic valve 17 connected to the compression chamber 24 of the high pressure pump 16, and the low pressure damper 12. The high pressure fuel supply apparatus 6 also includes a metal bellows 29 which substantially surrounds the cylinder 25 and the piston 26 and which prevents fuel which leaks out from between the cylinder 25 and the piston 26 from leaking to the outside of the apparatus 6.
The piston 26 is driven up and down in FIG. 9 by a drive cam mounted on an unillustrated camshaft, and fuel is sucked into and discharged from the compression chamber 24 by the movement of the piston 26. The electromagnetic valve 17 is opened when a prescribed amount of fuel is discharged into the common rail 9, so that some of the high pressure fuel within the compression chamber 24 is sent (released) to the inlet side rather than being sent under pressure to the common rail 9. By controlling the timing of opening of the electromagnetic valve 17, the amount of fuel discharged from the fuel supply apparatus 6 can be variably controlled.
Low pressure fuel from the fuel tank 1 passes through an intake valve 13 into the compression chamber 24, and is then discharged from the compression chamber 24 through a discharge valve 14. FIG. 10 is an enlarged view of region A of FIG. 9, showing a valve assembly including the intake valve 13 and the discharge valve 14, and FIGS. 11-16 show various portions of the valve assembly in detail. The valve assembly includes an upper plate 33, a lower plate 31, and a reed plate 33 sandwiched between the upper and lower plates 33 and 31. As shown in plan in FIG. 11, the upper plate 33 is a disk-shaped member having a relief flow passage 34 which communicates with the electromagnetic valve 17, two valve holes 35 which function as intake openings, and a cavity 36 which communicates with the discharge passage 23 and which has a size and shape so as not to interfere with the movement of a discharge valve reed 38 of the reed plate 32. As shown in plan in FIG. 12, the reed plate 32 is a thin disk-shaped member having two flat intake valve reeds 37 and a flat discharge valve reed 38. As shown in plan in FIG. 13, the lower plate 31 is a disk-shaped member having a cavity 39 which communicates with the compression chamber 24 and has a size and shape so as not to interfere with the movement of the intake valve reeds 37, and a valve hole 40 which functions as a discharge opening.
FIG. 14 is an enlarged plan view of the discharge valve reed 38 of FIG. 12, FIG. 15 is a cross-sectional elevation taken along line 15xe2x80x9415 of FIG. 14, and FIG. 16 is an enlarged cross-sectional elevation taken along line 16xe2x80x9416 of FIG. 14. The discharge valve reed 38 includes a flexible neck 42 and a disk-shaped head 43 which is secured to one end of the neck 42 and which can move between an open and a closed position to open and close the valve hole 40 of the lower plate 31. In FIG. 16, the dashed lines show the shape of the reed 38 in an unloaded state, and the solid lines show the shape when the discharge side of the valve assembly is at a higher pressure than the compression chamber 24 and the reed 38 is pressed against and closes the valve hole 40. The discharge valve reed 38 is strongly pressed by the high pressure P on the discharge side, so the reed 38 is deformed downwards at its center into the shape of a bowl such that the reed 38 is in sealing contact with substantially only the edge 41 of the valve hole 40. The amount of deformation of the reed 38 in its deformed state with respect to its shape in an unloaded state is H. The seal due to contact between the reed 38 and the edge 41 of the valve hole 40 is an edge seal involving line contact between the two members. This edge seal generates a large local stress in the seal portion of the discharge valve reed 38. Furthermore, the discharge valve reed 38 has a high stiffness at its neck 42, so the deformed shape of the head 43 when subjected to pressure is different where the head 43 adjoins the neck 42 than in other locations, so a gap develops in this region, and the sealing performance decreases (particularly at the border 44 of the neck 42 and the head 43). This same problem occurs with the intake valve reeds 37.
The thickness of the reed plate 32 is usually very thin, such as on the order of 0.3 mm, in order to decrease stresses generated at the time of valve opening and pressure losses. Therefore, in the device of FIG. 9, when the discharge pressure is set to a value such as 12 MPa, a defective seal can easily occur due to high stresses which are generated at the time of valve closing and deformation of reed 38, and damage to the reed plate 32 and a decrease in the discharge of the fuel supply apparatus 6 may occur. In the past, in order to cope with such problems, it was necessary to increase the thickness of reed 38 or decrease the diameter of the valve hole 40 in plate 33. However, in order to decrease pressure losses at the time of valve opening, it was necessary to elongate the neck 42 of the reed 38 or to increase the number of intake valves, so the high pressure fuel supply apparatus ended up being large in size. The same problem occurs with respect to the intake valve reeds 37.
The present invention provides a high pressure flow supply apparatus which can increase the stiffness of a valve reed without changing the thickness of a plate in which the reed is formed or the size of a valve hole covered by the reed, which can achieve a surface seal, and which can provide a valve having improved sealing properties and resistance to pressure.
According to one form of the present invention, a high pressure fuel supply apparatus includes a cylinder defining a compression chamber, a piston supported for sliding movement in the cylinder, and a valve communicating with the compression chamber. The valve includes a valve hole and a reed movable between an open and a closed position to open and close the valve hole. The reed has a head with an outer periphery in surface contact with a surface surrounding the valve hole when the reed is in its closed position, and a bulge surrounded by the outer periphery and extending away from the valve hole and disposed on the valve hole when the reed is in its closed position.
In a preferred embodiment, the bulge in the reed has generally the shape of a bowl.
The bulge in the reed preferably has a height which is at least 0.9 times the thickness of the reed.